Wet strength polymers

ABSTRACT

The invention provides a stable polymeric additive useful for improving the wet strength of a cellulosic substrate. The additive is a water-soluble cationic thermosetting polymer incorporating a plurality of extralinear glycidyl quaternary ammonium groups. The invention also comprises a method of making such an additive.

This is a division, of application Ser. No. 21,414, filed Mar. 19, 1979,now U.S. Pat. No. 4,233,417.

BACKGROUND OF THE INVENTION

This invention relates to novel additives for the production of wetstrength in cellulosic substrates. Untreated paper is essentially a massof cellulosic fibers held together by their physical contact withadjacent fibers and by hydrogen bonding between hydroxyl groups on thecellulosic polymer chains. Where such paper is placed in water theforces holding the fibers together are dissipated and the structurerapidly loses its coherency. This is a phenomenon that is familiar toall.

For some applications this behavior of wet paper is unsatisfactory asfor example when the paper is used to prepare kitchen towels, facialtissues, diaper liners, hand towels and the like. Accordingly, additiveshave been developed to improve the "wet strength" of such sanitarypaper. Such additives are usually applied in such a way that they adsorbonto the fibers of the paper and cure there such that the fibers are ineffect bonded together by the cured additive at the interfiber contactpoints.

DISCUSSION OF THE PRIOR ART

The wet strength additives of the prior art have taken a number of formsbut perhaps the most successful group have been based on the reaction ofamines with epihalohydrin, usually epichlorohydrin. The amines areusually described as polyamines and this term as used embraces polymerswith a plurality of amine groups and "monomers" such as hexamethylenediamine or iminobispropylamine that comprises more than one amine groupas well as "(pre)polymer condensates" prepared therefrom through the useof co-reactants such as α,ω-dihaloalkanes, acrylic esters and the like.For purposes of clarity polymers having a degree of polymerization inexcess of 5, comprising a plurality of amine groups will be referred tohereafter as "amine polymers" and it is this group particularly thathave provided most of the commercially successful wet strengthadditives.

In the above wet strength additives a portion of the amine groups hasbeen converted into epi-substituted amines, that is to say to produceamine groups with the structure: ##STR1## or the quaternary equivalentthereof.

The first form is the so-called "activated" form and the second the"stabilized" form. Which is present depends largely on the pH of theaqueous resin solution.

The generally accepted mechanism for the development of wet strength insuch systems is via intra/inter-molecular polycondensation crosslinkingreactions between free amine groups and amine groups bearing ahalohydrin or epoxy substituent or their quaternary equivalents, allpresent in the polymer structure.

It would appear that in such systems, the amine groups bearing theepoxide radicals react with other non-quaternized amine groups to formcrosslinks having the structure: ##STR2## or, where the epoxide-bearingamine group is quaternized and is reacted with a tertiary amine:##STR3## where A.sup.⊖ is any suitable anion. This same type of reaction(and reaction sequences leading to the reactant producing suchcrosslinks) is believed also to contribute substantially towardviscosity build-up during the preparation of conventional wet strengthadditives.

Wet strength additives of this sort are typified by U.S. Pat. No.3,855,158 which describes amine polymers, formed by reaction of aα,ω-diamine such as hexamethylene diamine with a α,ω-dihaloalkane suchas 1,2-dichloroethane, which are then reacted with epichlorohydrin.

The above types of amine polymer comprise for the most part a mixture ofprimary, secondary and tertiary amine groups. However, there are othertypes wherein all the amine groups in the polymer that are subsequentlyreacted with the epihalohydrin are tertiary amines and it is topolymeric additives produced by the reaction of epihalohydrins with suchpoly(tertiary amines) that this invention pertains.

One group of such additives is obtained by the reaction ofepichlorohydrin with the polymer formed by the polymerization ofN-methyl diallylamine and is described in U.S. Pat. Nos. 3,700,623,3,833,531 and 3,840,504.

Another type is that described in U.S. Pat. Nos. 3,694,393, 3,702,799and 3,842,054. These patents describe the reaction product of anepihalohydrin with a dimethylaminoalkyl (meth)acrylate ester.

A further polymeric additive type is described in U.S. Patent, now U.S.Pat. No. 4,222,92l, which describes the reaction product ofepichlorohydrin with polyvinylbenzyldimethylamine.

Whatever the chemical structure of the above amine polymers they allappear to gel rapidly by the crosslinking reaction described abovebetween quaternized amine groups bearing an epoxide group (as a resultof reaction with the epichlorohydrin) and remaining non-quaternizedtertiary amine groups in adjacent molecules. The reaction is triggeredby raising the pH of the polymer solution to a level of about 11-13,thereby activating the polymer. Such polymers are water-soluble,cationic and rapidly thermosetting.

The production of such polymers in alkaline solution must therefore becarefully monitored since the viscosity can build very rapidly withconsequent gelation. Obviously, this is undesirable since for maximumeffectiveness the polymer is preferably added as an aqueous solution tothe "wet end" of a paper machine producing wet strengthened grades ofpaper. The formation of gel at any time prior to wet web formation isusually unacceptable because it is inefficient and because of theprocess complications such gelation would cause both during andfollowing activation, especially in the system transporting theactivated polymer to the point at which it is added to the substrate.

To avoid gelation during synthesis or manufacture, the conventionalamine/epihalohydrin additives are prepared in alkaline solution but, assoon as the viscosity begins to rise rapidly toward incipient gelation,acid is added to short-stop (or "kill") the viscosity building reactionand the solution is diluted to a lower solids level to further reducethe tendency to gel. This final stage needs careful control and is anexpensive part of the process.

Reactions of the above type are relatively rapid and conventionally theconditions are such that a sizeable proportion of the epihalohydrinadded is lost through side reactions which do not result in theepihalohydrination of tertiary amine groups. It can be seen that whenthe epihalohydrin is used up and the reaction terminates there will be asubstantial proportion of non-quaternized amine groups remaining andthat these will react with glycidyl quaternary ammonium groups toproduce rapid gelation. By adding acid the epoxide groups are convertedto halohydrin groups which are very much more reluctant to undergo thecrosslinking reaction. However, directly the pH is raised to a level atwhich the polymer is once again activated, the tendency to rapidgelation returns.

It has been found that if essentially all the amine groups have beenconverted to glycidyl quaternary ammonium groups, the reaction leadingto gelation is not able to take place and the solution becomes stablefor prolonged periods even at a pH of 11 or more. In fact, if all aminegroups have been efficiently converted in this way, a 5-15% solidsaqueous solution will not gel for several hours or even days afteractivation at a pH of 11 or more. In contrast the products disclosed inthe prior art have a gel time that is counted in minutes. Thecompleteness of epihalohydrination of a polymer containing only tertiaryamine groups is therefore best judged by the time it takes the resultantpolyglycidyl quaternary ammonium salt to gel. This was not heretoforeappreciated and a number of patentees have described their products interms implying that quaternization by epihalohydrination had beencompleted. In fact, however, as is readily shown, the processesdescribed lead to a polymer containing a mixture of tertiary amines andglycidyl quaternary ammonium groups that gels comparatively quickly athigh pH. Examples of such patents include U.S. Pat. Nos. 3,694,393;3,842,054 and 3,702,799.

It has now been found that the reactions by which the quaternarypolymers are formed are extremely temperature dependent and that underthe conditions described in the prior art, a completely quaternizedpolymer cannot possibly be formed.

For the sake of brevity, all polymers in which substantially all aminegroups therein are quaternized and bear an epoxide group or a groupgenerating an epoxide in alkaline solution are hereinafter referred toas "perepiquat" polymers. They can be regarded as the products of theexhaustive perepichlorohydrination of polymers containing a plurality ofpendant tertiary amine groups.

The perepiquat polymers are themselves sensitive to temperature,especially after they have been activated at a pH of about 11. It isbelieved that this is a reflection of the occurrence of temperaturedependent intramolecular rearrangements generating species capable ofrapid reaction with other glycidyl quaternary ammonium groups to producea highly crosslinked intermolecular structure. Regardless of any theoryinvolved, it has been found that genuinely fully quaternizedpoly(tertiary amines) are characterized by very great resistance togelation at temperatures below about 25° C., even at high pH levels.Such polymers have extraordinary utility as, inter alia, wet strengthadditives for application to paper substrates. The betterrepresentatives develop more wet strength than the best availablecommercial additives applied at twice the application level.

The process for the production of perepiquat polymers described hereinalso has the advantage that it does not require "short stopping" by veryrapid acidification and dilution such that the polymers can be producedat reduced cost and handled more easily.

Since the perepiquat polymers are very pH-stable even after activation,they may be applied in solution at the "wet end" of a paper-makingmachine in much higher concentrations than has hitherto proved possiblewithout seriously exacerbating the problem of premature gelation. Thismeans that the ever-present fear of gelation in the transfer lines andtanks which is so common with conventional additives, especially if themachine has any prolonged "down-time" for any reason, is all buteliminated.

Despite their great stability to pH variations perepiquat polymers cureextremely rapidly in paper during the drying cycle, even under mildconditions. It is found that, using Noble and Wood handsheets in thelaboratory, very high "off-machine" cure is obtained.

A further advantage is that perepiquat polymers may be used inconjunction with various commercial amine polymer/epihalohydrinadditives to achieve any desired level of wet-strength. Thus, forexample, they can be used to boost the wet-strength for any particularpaper making run simply by adding the required amount to the regularwet-strength formulation without the need for equipment down-time beforethe high strength run is made.

Still another advantage of the perepiquat polymers is their utility asadditives for such light basis weight products as facial tissue,towelling and the like where low additive levels are preferred.

DESCRIPTION OF THE INVENTION

The invention comprises a process for the production of a water soluble,cationic, thermosetting wet strength additive which comprises reactingat a temperature of 20° C. or less an epihalohydrin and polymercomprising a backbone formed of repeating segments at least 10% of whichcomprise an amine group substantially all of said amine groups beingtertiary amine groups pendant from the backbone and having the structure

    Q˜N˜Z                                          [I]

where ˜Z is the number of bonds through which the nitrogen is linkeddirectly or indirectly through a hydrocarbyl radical, to the backbone;˜Q is the number of bonds by which the tertiary nitrogen is linked togroups selected from methyl and an alkylene group that, together withthe nitrogen, provides a heterocyclic group, with the limitations that Qis an integer from 0 to 2 and Z+Q is always 3; the ratio ofepihalohydrin groups to tertiary amine groups reacted being greater thanthe transition ratio (as hereinafter defined) for the reactionconditions selected.

As was indicated above this process produces polymers that are quitedifferent from those obtained using prior art processes and thisdifference is manifested primarily by the gel time of the polymers.Thus, while polymers having the above formula have been described, thereaction conditions described by the disclosers are such that in factthe transition ratio was not reached and the polymers obtained were notperepiquat polymers. The invention therefore also includes polymerswhich, on the evidence of their gel time, are indeed true perepiquatpolymers.

The present invention therefore also comprises a water soluble cationicthermosetting polymer comprising a backbone formed of repeating segmentsat least 10% of which comprise an amine group, wherein

A. substantially all the glycidyl quaternary ammonium containing groupsare pendant from the backbone segment and have the structure ##STR4##where -Z is the number of bonds through which the quaternary nitrogen islinked directly, or indirectly through a hydrocarbyl radical, to thebackbone segment; ˜Q is the number of bonds by which the quaternarynitrogen is linked to groups selected from methyl and alkylene groupthat together with the nitrogen, provides a heterocyclic group, with thelimitation that Q is an integer from 0 to 2 and Z+Q is always 3; and Ris selected from ##STR5## where X is a potential anion; and

B. a 10% solids solution of the polymer in water at 25° C. and a pH of11 does not gel for at least 10 hours.

It is understood that, under acidic conditions, the epoxy structure addsthe elements of H⁺ X_(H) ⁻, (X_(H) is a halogen), to give a halohydrinstructure which in turn will regenerate the epoxy structure when the pHis raised above 9. Polymers in which substantially all the2-hydroxy-3-halopropyl substituents on the quaternary ammonium groupstherein are converted in alkaline solution to the glycidyl quaternaryammonium structure described above, are likewise considered to be withinthe purview of this invention. The polymers in alkaline solution aresaid to be "base-activated" and cure more rapidly and fully than theircorresponding non-activated halohydrin counterparts.

The polymers are described as being water soluble but this should not betaken as necessarily indicating a total solubility at allconcentrations. Indeed, it may be appropriate, with certain polymers ofthe invention, to add them to the substrate to be treated in the form ofemulsions or dispersions. The term "water-soluble" then is to be takenas indicating at least a limited solubility in water and a characterthat is hydrophilic rather than hydrophobic.

The invention further comprises a process for improving the wet strengthof a fibrous cellulosic substrate which comprises applying to thesubstrate the base activated perepiquat polymer described above andallowing the polymer to cure in contact with the substrate.

It is an important feature of the process of the invention that theepichlorohydrination reaction temperature is not higher than 20° C. Theperepiquat polymers are most sensitive to temperature as they are beingformed and, at least during the time in which the major proportion ofthe reaction is taking place, the temperature must be maintained belowabout 20° C. and preferably from -5° to 20° C. Preferred maximumtemperatures during the reactions are below 15° C. such as about 10° C.or lower. Generally, the major proportion of the reaction occurs in thefirst 3 or 4 hours and after about 4 hours or more preferably afterabout 12 hours of the reaction, it is permissible to allow the reactiontemperature to increase to ambient temperatures or even higher. Forshort periods, the temperature can be raised as high as 40° C. if thereaction is essentially complete. There is however, little advantage inraising the temperature during the later stages of the reaction since,as has been indicated above, the perepiquat polymers are somewhattemperature sensitive and apparently undergo changes at temperturesabove about 25° C., especially at pH levels of about 11 or more to acomposition that behaves in a manner similar to prior artpolyamine/epihalohydrin reaction products. The speed of this change andtherefore the permissible time that may be spent above 25° C. depends onthe extent to which the 25° C. temperature is exceeded.

The emphasis in the above on the amino group not being part of thepolymer chain is significant. It would appear that the environment of anamine group that is to be reacted with the epihalohydrin is importantbecause attempts to form perepiquat polymers from certain amine polymerswith amine groups in the chain (intralinear amine groups) often resultsin rapid gelation. This apparently reflects a greater resistance toepihalohydrination of such intralinear amine groups, by comparison withknown polymers with extra-linear tertiary amine groups, with the resultthat there are many potential groups with which the glycidyl quaternaryammonium groups can react to form crosslinks leading to gelation. Sincethis gelation reaction is a faster reaction than theepichlorohydrination itself, there tends to be a rapid build up ofviscosity during the production phase once substantial numbers ofglycidyl quaternary ammonium groups have been generated, and rapidgelation ensues. The differentiating factor, as indicated above, isbelieved to be steric but, irrespective of the theory involved, suchintralinear amine groups should be substantially absent if the polymericadditives of the invention are to be obtained.

When the polyamine comprises pendant amine groups having two or moredifferent steric environments, this too can result in differentreactivities towards the epihalohydrin reactant and possibly some degreeof side reactions may take place. It is therefore, preferred that allpendant amine groups in the polyamine have substantially the samereactivity towards epihalohydrins.

THE TRANSITION RATIO

As indicated above, if an amine polymer in which substantially all ofthe amine groups present are pendant tertiary amines or theircorresponding salts is reacted with an epihalohydrin under traditionalmolar and/or equivalent ratios of epihalohydrin to amine groups (E/A)and temperatures, the alkali metal hydroxide activated polymer solutionwill gel in a matter of minutes at concentrations of about 10%.

It has now been found that if the E/A ratio is increased, the reactiontemperature is kept below about 20° C. and the reaction conditionsremain otherwise unchanged, a point is reached at which the time togelation of the polymer product increases enormously, often by two ormore orders of magnitude, over a very small change in E/A.

The "transition ratio" is defined as the E/A at which the gradient ofthe graph of gel time against E/A goes through a maximum.

The variation of gel time with E/A is graphically illustrated in FIG. 1of the drawings, attached hereto to facilitate the understanding of theabove definition. The graph represents a plot of gel time (on alogarithmic scale) in minutes against the E/A ratio (linear scale). Toobtain the graph 10% solutions of poly(N-methyldiallylamine) HClsalt/epihalohydrin condensate polymers made using different E/A ratiosand each caustic-activated to a pH of 11 to 12.5 or more, were observedto determine the time for the reaction mixture to gel (gel time) atambient temperatures and this time was plotted against the E/A ratioused. The polymers were formed under identical temperature gradientsbeginning with an initial temperature not greater than 10° C.

As can readily be seen, after a period of slow increase in gel timethere is a rapid jump from 10 to 1000 minutes over a range of E/A from1.58 to about 1.62 before the rate of increase begins to slow down. Themaximum rate of increase occurs at an E/A of about 1.60 and this is the"transition ratio" for that particular system.

It is found that the transition ratio depends on both the nature of thepolymer to be reacted with the epihalohydrin, the reactivity of thetertiary amines or salts thereof and steric factors associated with thetertiary amine functional group.

The transition ratio is also greatly dependent on the reactionconditions. As can be appreciated by monitoring the dichloropropanolby-product obtained after the amine polymer/epichlorohydrin reaction,some conditions are extremely wasteful of the epichlorohydrin reactant.Thus the pH level; the reaction temperature; the concentration of aminepolymer in the solution; the polyamine molecular weight and/orstructure; the anion species and/or its concentration; the length of thereaction; and the solubility parameters of the reactants (especially theepihalohydrin); all affect the efficiency of usage of theepichlorohydrin reactant and therefore change the effective E/A ratio.The use of a halid salt of the amine polymer also results in wastage ofepichlorohydrin, as is conclusively shown in U.S. application Ser. No.916,631, and this leads to a lower effective E/A ratio than thatcalculated on the basis of the reactants used. The effective E/A ratiocan also be affected by the presence of unreacted amine monomer afterthe polymerization process.

The transition ratio is particularly dependent on the temperature of thereaction and indeed it appears that above about 30° C. the transitionratio cannot be reached no matter how much the ratio of epihalohydrinadded to amine group content is raised. For efficient use of theepihalohydrin reactant it is important that the temperature of thereaction, particularly during the early stages when the major proportionof the quaternization reaction takes place, be maintained below about20° C. such as from -5° to 20° C. and preferably around 10° C.

Thus, in summary, the transition ratio is a characteristic of thespecific reaction by which the perepiquat polymer is made. In practicethe reaction conditions preferred for the process of the invention aresuch that permit the most efficient use of the epihalohydrin reactant.This conventionally means operating at a pH of between 7.5 and 9.5 andmore preferably between 8 and 9. However, for very reactive polyamineintermediates the reaction may require moderating by a reduction of thepH to about 4 to 7. This has the effect of increasing the amine saltconcentration at the expense of the free amine groups thus raising theapparent E/A ratio which of course is calculated on the basis of free ortheoretical amine equivalency. The reaction will be self-sustainingsince each amine reacting will generate a hydroxyl ion that will in turnfree another amine group for reaction.

Other preferred conditions include a reaction temperature of betweenabout -5° and 20° C. and preferably from 5° to 15° C.; and a totalsolids percentage figure for the reaction of between 10 or preferably 20and 50% and most preferably 25-35%. The transition ratio in practicedefines the minimum E/A that will permit generation of a perepiquatpolymer and also indicates the efficiency of the usage of theepihalohydrin in the reaction. Thus, the lower the transition ratio, themore efficient is the utilization of the epihalohydrin. The preferredtransition ratio is less than 1.8 and, more preferably still, belowabout 1.5.

The preferred conditions for the process of the invention are thosewhich result in an epihalohydrin conversion figure of at least 60%(calculated as shown in Table 1 below) and most preferably at least 70%.

As will be appreciated the theoretical value of the E/A ratio forformation of perepiquat polymers is 1.0. However, as indicated above thereaction of the epihalohydrin with the amine is not the only reactionthat can occur during epihalohydrination. The chief competing reactionis with free halide ion in the presence of water to produce the twoisomeric dichloropropanols but other byproducts can include3-chloro-1,2-propane diol, glycidol, glycerol and the like.

If therefore, the E/A ratio charged is multiplied by the percentageconversion of the epihalohydrin, the new ratio, called herein the E/A(effective), should approximate 1 if in fact a peripiquat polymer isobtained. As will be seen from the Examples hereinafter presented thisis indeed found to be the case.

THE POLYMERIC ADDITIVE

The perepiquat polymers of the present invention are formed by thereaction of an epihalohydrin with an amine polymer wherein substantiallyall the amine groups in the polymer are extralinear tertiary amineswhich are not part of the polymer chain or backbone.

Typical examples of amine polymers that can be used to produce theperepiquat polymers include polymers and copolymers ofN-methyldiallylamine which contain the repeating group: ##STR6## and thecorresponding polymers or copolymers where an N-substituted diallylamineis used.

In polymers such as the above in which "Z", (the number of bonds linkingthe nitrogen atom directly or indirectly to the polymer backbone), is 2and the nitrogen is part of a cyclic group the "backbone" portion of thecyclic group is taken as being the shortest route around the group inaccordance with the conventional usage.

Other preferred polymers are typified by those having repeating unitswith the structure: ##STR7## similar homologous units.

Yet other amine polymers are those formed by polymerizing (includingcopolymerizing) the following monomers ##STR8## as well as homologues ofsuch monomers.

In each case the perepiquat polymer is formed by reacting the tertiaryamine-group containing polymer as its partial salt with epihalohydrin attemperatures below 20° C. under such conditions that substantially allthe amine groups are quaternized by alkylation with epihalohydrin.

The amine polymers used in the invention are generally homopolymers butin many cases the presence of up to 90% molar of a comonomer which doesnot adversely affect the water solubility of the polymer can addspecific advantageous properties to the polymeric additive. These can bechemical and/or physical in nature, and can ultimately convey eitherenhanced paper properties such as softness, tear resistance, absorbancy,creping, printability and the like; or they can facilitate the paperproduction process by enhancing drainage, fines retention, dyereceptivity, Yankee drier release and/or adhesion characteristics andresistance to foam generation. The use of such monomers to formcopolymers with the above amine monomers are therefore also within thepurview of the invention.

The comonomers that can be used to produce the perepiquat polymers asindicated above should not be such that the water solubility oremulsifyability characteristics of the polymer are lost. In addition tothat limitation, it is only required that in the case of vinyl, allyland related monomers which undergo anionic, cationic or free radicalpolymerization, the comonomer contain one monoethylenically unsaturatedgroup capable of copolymerizing with the unsaturated group of thetertiary amine or tertiary amine salt monomer. Suitable groups ofcomonomers among the many available include mono-unsaturated acids suchas acrylic acid as well as the esters, nitrile and amide derivatives ofsuch acids; mono-unsaturated alcohols and esters of such alcohols;mono-unsaturated ethers and ketones; and mono-unsaturated hydrocarbons(though below levels which would make the polymer water insoluble asindicated above). Other acceptable mono-unsaturated monomers includevinyl esters, amides, lactams, ethers and the like.

The essential characteristic of the cationic thermosetting polymers whenused as wet strength additives is that they are water soluble and thatsubstantially all the original tertiary amine groups present have beenconverted to quaternary groups with an epoxy substituent. The only otherpractical limitation involves the ability of the comonomer tocopolymerize with the monomer bearing the amine group through amechanism not involving the amine group. Generally both monomer andcomonomer should respond to a common initiating catalyst or catalystsystem.

The perepiquat polymers are obtained by the reaction of such aminepolymers with an epihalohydrin. This may be for example epichlorohydrin,epibromohydrin or epiiodohydrin but in practice the one most oftenpreferred is epichlorohydrin.

USE OF POLYMERIC ADDITIVE AS WET STRENGTH ADDITIVES

The perepiquat polymers can be applied to a fibrous cellulosic substrateeither at the wet end, i.e. to an aqueous slurry of the cellulosicfibers or they can be sprayed onto a cellulosic fiber wet. Size pressaddition is also a feasible alternative. The treated substrate is driedand then cured by heating for a brief period, usually less than 10 to 15minutes at about 90°-100° C. in an aircirculating oven. Under actualpaper mill conditions, where contact time between wet felt-pressed wetand "Yankee" or can driers is in the order of seconds, efficient curingnevertheless occurs. The time required for development of good strengthis therefore quite short.

Other additives commonly used in the production of paper such as alum,pitch dispersants, dry strength resins, starches, gums, softening agentsand Yankee release and coating aids, may be added before or after thewet strength additive of the invention providing there is no interactionbetween the two that would affect the thermoset curing mechanism.

The levels of perepiquat polymer addition are nearly always very muchlower than those typically used with prior art polymers to obtain asimilar level of wet strength, often only half the usual amount beingrequired. As a guide the polymer can be added at a level of from 0.5 to20, but preferably 2 to 10, kilos per metric ton of substrate weight andstill give excellent results. This feature is very dramaticallyillustrated in the accompanying Examples presented below.

In the alternative embodiment the perepiquat polymers may be used inconjunction with a wet strength additive of the conventional kindproduced by the reaction of an epihalohydrin with a polyamine at an E/Aratio below the transition ratio. This has the effect of boosting theeffectiveness of the conventional additive to a level intermediatebetween its usual level of performance and that available using theperepiquat polymer alone. The proportions of the two components areconventionally in a weight ratio of from 90:10 to 10:90. Alternatively acompound comprising a plurality of amine groups may be used, in the sameproportions, in place of the conventional wet strength additive. Theamount of such mixture used to convey wet strength to a cellulosicsubstrate can be, for example, from 2 to 20 kilos/metric ton.

DESCRIPTION OF THE DRAWINGS

FIG. I is a graph of gel time (on a logarithmic scale) against E/A forthe polymers produced by reaction of poly(N-methyldiallylamine)hydrochloride with epichlorohydrin.

FIG. II is a plot of E/A (effective) against the gel time using the datafrom FIG. I adjusted to E/A (effective) as opposed to E/A as charged.

FIG. III is a similar graph to that of FIG. I except that the polyamineis poly(vinylbenzyldimethylamine) hydrochloride.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The invention is further illustrated by reference to Examples whichdescribe the production and testing of various perepiquat polymers andcompares the results obtained with other compositions that do not fallwithin the definition of this invention.

EXAMPLE 1

This Example describes the preparation of a typical wet strengthadditive according to the invention. This method is adaptable to theproduction of other additives with suitable adjustments of chargequantities and perhaps reaction times.

The amine polymer used as the basis for the reaction is apoly(N-methyldiallylamine.hydrochloride salt) from which unreactedmonomer has been removed, and the epihalohydrin is epichlorohydrin.

A charge of 184.64 g (0.500 amine equivalents of partially causticsoda-neutralized polyamine salt, 80.96 g (0.875 moles) ofepichlorohydrin and 369.49 g of deionized water is charged into a4-necked one liter reaction vessel fitted with addition funnel,thermometer, agitator and condenser. The E/A of the charge was therefore1.75 and the reaction mixture contained 25% total theoretical solids.

The temperature of the initial reaction mixture was 10° C., the pH was8.14 and the epichlorohydrin was added to the polyamine/water mixturewith stirring over a period of 30 seconds. After 3 hours the temperaturewas allowed to rise slowly to room temperature overnight.

Eighteen hours after the reaction began the resultant solution was veryclear, pale yellow in color, the pH was 8.14 and the Gardner viscositywas A. The viscosity and pH did not change perceptibly during a furtherfour hours so that the reaction was considered finished and acid wasadded to reduce the pH to 1.19.

The reaction product had a Gardner viscosity of B⁻ /B and the yield was82.8% of theoretical. The epichlorohydrin conversion was calculated tobe 65.9%.

The polymer, held at ambient temperatures (about 25° C.), was found tobe non-gelling at pH of about 11 to 12.5 for about 48 hours. By contrasta leading commercial wet strength additive, ("S-2064", produced byHercules, Inc.) based on the same polyamine but reacted withepichlorohydrin at a E/A ratio below the transition ratio, gels in about6 minutes at the same temperature and solids content.

The reaction was repeated essentially as described above at a number ofE/A ratios and for each the gel time was measured. The gel time was thenplotted against the E/A ratio and the graph appearing as FIG. I wasobtained. As can clearly be seen the transition ratio has a value ofabout 1.60.

The E/A (effective) calculated as described above was then plottedagainst gel time again using a semi-log graph and the results are shownin FIG. II. From that it can be seen that the E/A effective at thetransition point is about 1.12 or reasonably close to the theoretical1.0 value.

EXAMPLE 2

This Example describes the production of a perepiquat polymer by thereaction of poly(vinylbenzyldimethylamine) hydrochloride salt withepichlorohydrin.

A reaction vessel was charged with 161.3 g (1.0 mole) of distilledvinylbenzyldimethylamine monomer and 400 g of deionized water. Thetemperature was maintained at 5°-9° C. during the dropwise addition of96.3 g (approxmately 1.0 mol) of 38% hydrochloric acid.

The final pH was adjusted to 4.7 and the salt was freed from inhibitorsby four extractions using fresh 30 ml portions of dichloromethane.

The aqueous solution was then stirred in a four-necked flask overnightwith air entrainment to remove traces of dichloromethane vapor.

The flask was then fitted with stirrer, thermometer, condenser and themeans to bubble nitrogen through the reaction mixture. To this mixturewere added 5.0 g of ammonium persulfate. The weight of the reactionmixture was adjusted to 675.7 g (30% total solids). The reaction mixturewas stirred and blanketted/sparged with nitrogen at 20° C. for 30minutes before heating was begun. The temperature was then rapidlyraised to 70° C. at which level it was held by air jet cooling. About anhour after reaction began the exothermic reaction subsided and thereaction mixture was maintained at 70° C. for a further two hours byexternal heating.

The polymerization mixture was a clear light yellow solution and had aGardner viscosity of about L at about 30% total solids. The pH at 25° C.was 1.36.

The monomer to polymer conversion was calculated to be 100.9%.

The polymer solution so prepared, which weighed 67.57 g and contained20.53 g (0.100 amine monomer unit equivalents) of polymer solids, wasplaced in a reaction vessel with 13.52 g of deionized water and wasneutralized by the dropwise addition of 36.0 g (0.018 equivalents) of2.0% aqueous hydroxide, with continuous stirring.

The temperature of this mixture was 10° C. and the pH was 7.56.

While the mixture was kept cooled and stirred 11.1 g (0.12 mole) ofepichlorohydrin were added over a period of 30 seconds. The temperaturewas allowed to rise slowly over a five hour period to 20° C. at whichtime the pH was 8.48 and the Gardner viscosity was A⁺ /B⁻.

The reaction mixture was stirred at room temperature overnight and thefollowing day the reaction was stopped by addition of 0.5 g of 96%sulphuric acid, thereby dropping the pH from 7.59 to 1.10.

The Gardner viscosity of the product was B⁻ /B at a total solids of 24%.The percentage theroretical yield was 102.3%. Similar productions atdifferent E/A ratios were carried out and in each case the gel time at apH above 11 was determined in the manner described above.

The gel times obtained were plotted against the corresponding E/A togive the graph appearing at FIG. III. of the Drawings. Again a period ofrapid increase of gel time over a comparatively short range of E/A isobserved. The transition ratio is estimated to be about 1.1.

It is significant that this result is very close to the theoretical E/Aratio of 1.00, showing that the conditions chosen were such that theside reactions tending to waste the epichlorohydrin reactant weredisfavored by the reaction conditions.

EXAMPLE 3

Essentially the same procedure as is described in Examples 1 and 2 isused to produce other additives according to the invention. Thereactions are summarized in Table 1 below.

Polymers of 1-3 are the same as those produced in Example 1 except forthe E/A ratio. Polymer 4 basically the same as Polymers 1-3 except thatthe sulphuric acid salt is used in place of the hydrochloric acid saltto prepare the polyamine.

Polymer 3 is that described in Example 1.

Polymers 5 and 6 are derived from the reaction ofpoly(vinylbenzyldimethylamine)hydrochloride with epichlorohydrin using aprocess substantially as described in Example 2 adjusted to conform tothe different E/A ratio.

In each case the reaction was initiated at 10° C. and allowed to reachthe higher temperature during the course of the reaction. Polymers 1 and4 were raised to 40° C. after 19 and 24 hours of reaction time i.e.,after the reaction was essentially complete. Prior to that the reactiontemperature had been around 20° C.

                                      TABLE I                                     __________________________________________________________________________                   Polymer                                                                            Polymer                                                                            Polymer                                                                            Polymer                                                                            Polymer                                                                            Polymer                                              1    2    3    4    5    6                                     __________________________________________________________________________    POLYMER PREPARATION                                                           E/A Ratio (1)   2.0  1.70                                                                               1.75                                                                               1.80                                                                               1.50                                                                               1.50                                 Run Conc., % (2)                                                                             25%  25%  25%  30%  25%  25%                                   Rxn Temp., C°.                                                                        10-40°                                                                      10-21.8°                                                                    10-20°                                                                      10-40°                                                                      10-25°                                                                      10-22.5°                       NaOH, Eq. %     0    0    0   12.5  0    0                                    Run pH (3)     8.22-7.48                                                                          8.63-8.10                                                                          8.62-8.10                                                                          8.91-7.07                                                                          8.18-7.54                                                                          8.21 -7.51                            Kill Visc., Gardner                                                                          A-1  B    A      -- A-1  A-1                                   Rxn Time, hrs. 22:00                                                                              22:00                                                                              23:00                                                                              27:00                                                                              24:00                                                                              24:00                                 POLYMER PROPERTIES                                                            pH 25° C.                                                                              2.95                                                                               2.38                                                                               2.23                                                                               2.57                                                                               2.74                                                                               2.89                                 Viscosity Gardner (4)                                                                        A-1- B+   B.sup.- /B                                                                         F.sup.- /F                                                                         A-1.sup.-                                                                          A-1.sup.-                             T.S. %         16.44%                                                                             21.12                                                                              20.64                                                                              25.97                                                                              16.44                                                                              22.64                                 Resin Yield, % (5)                                                                           77.9%                                                                              86.0 82.8 92.7 77.9 88.8                                  Epi Conversion, % (6)                                                                        67.2%                                                                              66.2 65.9 84.3 67.2 74.6                                  %DCP @ T.S. Found                                                                             4.90%                                                                              5.48                                                                               5.70                                                                               2.40                                                                               3.60                                                                               3.53                                 __________________________________________________________________________     (1) Moles epi/total amine monomer unit equivalents.                           (2) Total organics charged/resin solution weight                              (3) General profile: initial pH 7.5-8.1, increasing to the max. value         within 3-4 hours, then gradually falling off to 8.0.                          (4) % T.S. found                                                              (5) (Experimentally determined total solids/theoretical total "solids"        charged) × 100.                                                         (6) Determined as follows:                                                    Epi Conversion                                                                ##STR9##                                                                      ##STR10##                                                                

EXAMPLE 4

This Example describes the method by which the perepiquat polymers whoseproduction is described in Example 3 were tested for wet strength anddetails the results obtained.

In each case a pulp slurry of a 50/50 blend of bleached hardwood andbleached softwood Kraft fibers with a pH of 7.0 and a Canadian StandardFreeness of 457 was prepared. To volumetrically measured samples of thisslurry were added, with stirring, measured aliquot amounts of one of thepolymers produced in Example 3. Prior to addition to the pulp slurry thepolymers, at concentrations of from 3 to 10%, were activated by theaddition of 7.0 meq of 25% aqueous sodium hydroxide per gram of resinsolids during 15 seconds. The mixture was stirred throughout theaddition and thereafter at room temperature for one minute before beingdiluted to 1.2% concentration by addition of more deionized water.

Enough of the activated resin solution was added with stirring to thepulp slurry to correspond to an application level of 5.0 kilos permetric ton. The treated pulp slurry was then allowed to stand at roomtemperature for 10 minutes before being made into hand sheets.

The treated fibers were formed into a wet laid web with a pressconsistency of 36.1% and dried for 2 minutes at 96° C. The resulting 2.5g 20.3×20.3 cm Noble and Wood hand sheets were left at constanttemperature and humidity for one day before being cut into 2.5 cm×20.3cm strips and tested for tensile strength on an Instron Tensile Tester.Half of each group of samples was tested after being cured for 15minutes at 90° C. in a circulating oven and then water soaked for 10minutes. The other half omitted the curing process and thus representsuncured, "off-machine" test sheets.

The results are set forth in Table II below. It should be noted that thepolymers 1 and 4 where the reaction temperatures were raised to 40° C.for 3 hours at the end of the reactions perform somewhat worse than theothers that never exceeded 25° C.

                  TABLE II                                                        ______________________________________                                        WET TENSILE STRENGTH                                                                   WET TENSILE STRENGTH* (gm/cm)                                        POLYMER    Uncured (U) Cured (C)  U/C Ratio                                   ______________________________________                                        1          829          989       0.838                                       2          852         1039       0.820                                       3          893         1102       0.810                                       4          755          979       0.772                                       5          857         1014       0.845                                       6          857         1034       0.829                                       ______________________________________                                         *Average of 4 pulls on an Instron Tensile Tester.                        

EXAMPLE 5

This Example describes the results of comparing the wet strengthefficiency of a commercial wet strength additive prepared by the priorart methods with a perepiquat polymer made using the same reactants butwith an E/A above the transition ratio.

Both polymers were produced by the reaction ofpoly(N-methyldiallylamine) hydrochloride with epichlorohydrin. Thecomparative example was "S-2064", a wet strength additive supplied byHercules, Inc.

The polymer of the invention was "Polymer 3" described in Example 2.

Both polymers were activated with caustic soda in the manner describedin Example 4.

The polymers were applied in the manner described in Example 4 exceptthat the pulp had a Canadian Standard Freeness of 450.

The results are set forth in Table III below.

                  TABLE III                                                       ______________________________________                                                Comparative Wet Tensile Strengths*                                            (gm/cm)                                                                       Uncured (U)                                                                             Cured (C)   U/C Ratio                                       ______________________________________                                        Polymer 3 956         1102        .867                                        "S-2064"  732          882        .830                                        ______________________________________                                         *Average Level 5.0 kilos/metric ton. Tensile strengths are average of 4       pulls on an Instron Tensile Tester.                                      

As can be seen from the above data, the perepiquat polymers have avastly superior effectiveness as wet strength additives in addition tohaving a greatly extended gel time.

EXAMPLE 6

This Example compares polymer 3 (from Example 2) to two commercial wetstrength additives, Kymene 557 H and Kymene 557 M, for efficiency."Kymene" is a trade name of Hercules Company. Kymene 557 H and 557 M areepichlorohydrin-bodied polyaminoamide resins of the kind described inU.S. Pat. Nos. 2,926,116; 2,926,154; 3,058,873; 3,724,986 and 3,240,761.

The test method was that given in Example 4 except that the pulp finishwas 80% bleached softwood Kraft/20% bleached hardwood Kraft. TheCanadian Standard Freeness was 550, and the basis weight was 0.311kg/sq. meter (210 pounds/3300 sq.ft. ream). The pH of the pulp was 7 andthe hardness was 100 ppm.

Before addition to the pulp each polymer was activated in solution at10-12% polymer solids using 7.0 meq/g of 50% aqueous sodium hydroxidefollowed by dilution to 5% concentration using deionized water.

The wet tensile strength results obtained are given in Table IV. Each isthe average of four pulls on an Instron Tensile Tester.

                  TABLE IV                                                        ______________________________________                                                            Wet Tensile Strength                                                Application Level                                                                         (gm/cm)                                                 Polymer     kilos/metric ton                                                                            Uncured   Cured                                     ______________________________________                                        Polymer 3   1.5           1893      1929                                                  3.0           2840      3108                                      Kymene 557 H                                                                              2.5           1945      2179                                                  5.0           2661      3000                                                  7.5           2822      3179                                      Kymene 557 M                                                                              2.5           1572      1822                                                  5.0           2161      2411                                                  7.5           2358      2661                                      ______________________________________                                    

Thus, it can clearly be seen that Polymer 3 at 3.0 kilos/metric tonperforms comparably in both cured and uncured tests to Kymene 557 H at7.5 kilos per metric ton and much better than Kymene 557 M at thatlevel. Expressed differently the level of performance of Kymene 557 H isachieved using "Polymer 3" at only 40% of the Kymene 557 H applicationweight.

EXAMPLE 7

This Example illustrates the versatility of the polymers of theinvention in producing a wet strength additive of the traditional typewith enhanced effectiveness.

In the reactions described below, a compound comprising a plurality ofamine groups was added with stirring to a cooled dilute perepiquatpolymer. In each case acid short-stopping was required when theviscosity began to build.

It seems clear that these mixed polymers represent products somewhatsimilar to the polymers of the prior art in that the curing is theresult of the reaction of "epi" groups contributed by the perepiquatresin with the amine groups on the amine polymer.

The process for the production of the blends is summarized in Table Vand the properties are set forth in Table VI.

                                      TABLE V                                     __________________________________________________________________________    PREPARATION OF POLYMER BLENDS                                                             A       B    C   D    E     F    G                                __________________________________________________________________________    Perepiquat polymer                                                                        2       3    3   3    4     6    6                                Amine containing                                                                          DCE/HMD (1)                                                                           PET (2)                                                                            tetra-                                                                            Amine                                                                              Diethylene                                                                          DCE/ Diethylene-                      additive                 methyl                                                                            polymer                                                                            triamine                                                                            HMD (1)                                                                            triamine                                                  HMD used in                                                                       (3)                                              E/A (5)     1.3     1.4  1.0 1.4  1.3   1.3  1.10                             Run concentration (%)                                                                     15      15   15  22   17.5  17.5 20                               Reaction Temp (°C.)                                                                10-15   10-20                                                                              10-30                                                                             10-30                                                                              10    10-30                                                                              10-30                            NaOH Equivalent %                                                                         0       0    0   125  0     0    0                                Run pH      10.8.73 9.11-8.82                                                                          9.82-                                                                             8.65-                                                                              10.35-                                                                              10.12-                                                                             10.05-                                                    9.29                                                                              7.38 9.46  8.26 8.75                             Gardner Viscosity at                                                          kill        D+      H    H   H    L/M   E/F  F/G                              Reaction time (hrs.)                                                                      1:45    1:20 1:35                                                                              4:15 2:0   2:45 1:25                             pH at 25° C.                                                                       2.04    1.68 2.17                                                                              2.09 2.34  2.24 1.86                             Gardner viscosity                                                                         C       I/I.sup.+                                                                          H   D.sup.+                                                                            R     E/E.sup.+                                                                          G.sup.+                          Total solids %                                                                            16.27   12.64                                                                              14.35                                                                             17.48                                                                              12.2  17.25                                                                              16.56                            Resin yield %                                                                             104.4   103.7                                                                              103.2                                                                             104.7                                                                              103.7 103.4                                                                              104.2                            % DCP at % T.S.                                                                           2.40    2.27 1.42                                                                              3.28 0.48  1.3  1.4                              found (4)                                                                     __________________________________________________________________________     (1) Reaction product of dichloroethane with hexamethylene diamine in a        ratio of 0.75:1 after halide has been removed from the amine polymer          produced                                                                      (2) Polyethylene imine (commercial)                                           (3) N,N,N',N"-tetramethyl1,6-hexamethylene diamine                            (4) % Dichloropropanol at the total solids found.                             (5) Theoretical epiquat equivalents in the perepiquat polymer/amine           equivalents in amine prepolymer.                                         

                  TABLE VI                                                        ______________________________________                                        WET TENSILE STRENGTHS OF POLYMER                                              BLEND CONDENSATES (1)                                                               Application Level                                                                          Uncured Tensile                                                                            Cured Tensile                                 Blend (kilos/metric ton)                                                                         Strength(gm/cm)                                                                            strength(gm/cm)                               ______________________________________                                        A     2.5          493          688                                                 5.0          654          843                                                 7.5          763          948                                           B     2.5          557          736                                                 5.0          670          843                                                 7.5          686          970                                           C     2.5          436          572                                                 5.0          645          822                                                 7.5          757          893                                           D     2.5          552          755                                                 5.0          711          922                                                 7.5          800          1011                                          E     2.5          423          614                                                 5.0          664          891                                                 7.5          805          1006                                          F     2.5          475          691                                                 5.0          645          882                                                 7.5          779          973                                           G     2.5          480          654                                                 5.0          734          897                                                 7.5          857          1009                                          ______________________________________                                         (1) Average of 2 pulls on an Instron Tensile Tester.                     

The application and testing procedure was that outlined in Example 4.

EXAMPLE 8

This Example illustrates the extreme temperature dependence of thereaction to produce the perepiquat polymers.

Two reactions were conducted side-by-side under substantially identicalconditions apart from the reaction temperature. In the first, thereaction was initiated at 10° C. and allowed to rise no higher than 13°C. In the second, the reaction was initiated and maintained at 25° C.

The reactants in each case were epichlorohydrin andpoly(N-dimethylaminoethylmethacrylate.HCl salt) with an E/A ratio(charged) of 1.25 and the polymers were activated at 10% solids solutionand room temperature using 25% NaOH at 7 meq/g.

The polymer produced at 25° C. had a gel time of 230 minutes whereas theone produced at 10°-13° C. had a gel time of 1530 minutes.

From these results it can clearly be seen that at the lower reactiontemperatures the transition ratio had clearly been exceeded and a trueperepiquat polymer obtained whereas at the higher temperature thetransition ratio had still not been reached and the polymer failed toreach the same high level of stability that characterizes perepiquatpolymers.

EXAMPLE 9

This Example illustrates the temperature dependence of the sodiumhydroxide-activated polymer produced in Example 1.

Two samples of the polymer at 25° C. were adjusted to 10% solidsconcentration and activated to a pH of 12+, (autogenously decreasing to11 during the course of the reaction), using caustic soda.

The first sample was heated to 50° C. and the second was kept at 25° C.

The first gelled after 15.33 minutes and the second after 4320 minutes.

This shows the extreme sensitivity to temperature of activatedperepiquat polymers.

EXAMPLE 10

This Example illustrates the temperature dependence of the reaction bywhich perepiquat polymers are obtained.

Three polymers A, B and C based on the reaction of epichlorohydrin withpoly(N-methyldiallylamine.HCl salt) are prepared at an E/A (charged)ratio of 1.70. The initial reaction conditions were identical with thetemperature 20° C. and the pH 7.82.

Polymer A was produced at a reaction temperature that was reduced to,and maintained at, 15° C. Polymer B was produced at a temperature thatwas raised to, and maintained at, 30° C. Polymer C was produced at 50°C. and held at that temperature until it was necessary to kill thereaction by the addition of acid to prevent gelation.

Polymers A, B, and C, simultaneously activated as solutions with a 10%solids concentration using 25% aqueous sodium hydroxide, had gel timesof 1710 minutes, 70 minutes and 4 minutes 20 seconds, respectively.

This clearly shows that the Polymer A was a true perepiquat polymerwhereas Polymers B and C were not.

EXAMPLE 11

This Example describes the effect of temperatures on the gelation timeof a copolymer.

A 50/50 molar copolymer of vinylbenzyldimethylamine (partialhydrochloride salt) with acrylamide was reacted with epichlorohydrin atan E/A of 1.20 under two different temperature conditions. The firstreaction was conducted in essentially the manner described in Example 2.The second reaction was substantially identical except that the reactionwas carried out at 25° C.

The gel times for identically caustic activated 10% solids solutions ofeach were measured. The polymer produced under the conditions set forthabove for the production of a perepiquat polymer gelled in 630 minuteswhereas the one prepared at 25° C. gelled in 31 minutes.

The above results indicate clearly that the presence of a comonomer doesnot interfere with the phenomenon described herein.

EXAMPLE 12

One of the advantages of the perepiquat polymers of the invention istheir compatibility with conventional caustic-activated wet strengthadditives. They can therefore be used to enhance the efficiency of suchconventional additives without loss of any of their beneficialproperties.

This Example describes the effectiveness of blends of a perepiquatadditive with a conventional additive in varying proportions.

The first component of the blend was a perepiquat polymer obtained by areplication of the reaction used to produce Polymer 3 of Example 3(above) with the minor difference that the reaction was initiated at 5°C. and was allowed to rise to 15° C. after 3 hours. The analysis of thereaction product showed a slightly lower conversion of epichlorohydrin.

The second component of the blend was a commercial wet strength additiveobtainable from Monsanto Company under the Registered Trade Mark"Santo-Res" 31 (SR-31). This is a reaction product of epichlorohydrinand an amine prepolymer obtained by a process comprising the reaction ofan alkylene diamine and a dihaloalkane.

The perepiquat resin was used as a 20.7% total solids solution and theSanto-Res 31 as a 24.5% total solids solution.

The components were blended to give the desired weight/weight ratios andthen diluted to 4.0% total solids concentration. The solutions wereactivated by addition of 7.0 meq/gram of 25% sodium hydroxide over 5-10seconds.

After one minute of stirring the activated solutions were diluted to1.2% concentration of the activated additive blend using deionizedwater.

These solutions were then screened for uncured and cured (15 minutes at90° C. in a circulating air oven) wet tensile strength using standard"Noble and Wood" handsheet papermaking conditions. Three addition levelswere used in the evaluation and the results are set forth in thefollowing Tables VII, VIII and IX.

                  TABLE VII                                                       ______________________________________                                        ADDITIVE WET TENSILE STRENGTH EFFICIENCY                                      COMPARISON UNCURED                                                            Blend                                                                         Wt. % of Wt. % of   Summed Wet (3)                                                                              % of                                        PEQ (1)  SR-31 (2)  Strength (gm/cm)                                                                            Control                                     ______________________________________                                        --       100 (control)                                                                            1929          100%                                        20       80         2209          114.5%                                      40       60         2406          124.7%                                      60       40         2499          129.5%                                      80       20         2672          138.5%                                      100       0         2692          139.5%                                      ______________________________________                                         (1) "PEQ" indicates the perepiquat polymer component.                         (2) "SR31" indicates the SantoRes 31 component.                               (3) This column is a cumulation of the average wet strength of three          samples at each of three different levels of application: 2.5, 5.0, and       7.5 Kg of the blend per metric ton of paper substrate.                   

                  TABLE VIII                                                      ______________________________________                                        ADDITIVE WET TENSILE STRENGTH EFFICIENCY                                      COMPARISON CURED                                                              Blend                                                                         Wt. % of Wt. % of   Summed Wet    % of                                        PEQ      SR-31      Strength (gm/cm)                                                                            Control                                     ______________________________________                                        0        100        2842          100%                                        20       80         3043          107%                                        40       60         3243          114%                                        60       40         3301          116%                                        80       20         3402          120%                                        100      0          3447          121%                                        ______________________________________                                    

The column headings in this Table have the significance set forth belowTable VII.

TABLE IX

This Table sets forth the average ratio of uncured to cured wet strengthfor each blend at the three levels of addition used. It clearly showsthat PEQ additives give a higher degree of development of wet strengthwithout cure than do conventional additives.

                  TABLE IX                                                        ______________________________________                                        UNCURED/CURED WET TENSILE STRENGTH RATIO                                      Wt. % Wt. %    Addition Level                                                                            Uncured/Cured                                                                           Average                                  PEQ   SR-31    Kg/metric ton                                                                             W.T.S. Ratio                                                                            U/C Ratio                                ______________________________________                                        0     100      2.5         0.634     0.673                                                   5.0         0.662                                                             7.5         0.722                                              20    80       2.5         0.690     0.722                                                   5.0         0.721                                                             7.5         0.755                                              40    60       2.5         0.693     0.739                                                   5.0         0.781                                                             7.5         0.744                                              60    40       2.5         0.760     0.758                                                   5.0         0.776                                                             7.5         0.738                                              80    20       2.5         0.751     0.784                                                   5.0         0.794                                                             7.5         0.806                                              100   0        2.5         0.819     0.778                                                   5.0         0.742                                                             7.5         0.774                                              ______________________________________                                    

The results set forth above in Tables VII to IX show clearly that thereis substantial advantage to be gained by using the perepiquat additivesin conjunction with known alkali-activated wet strength additives. Thismethod provides a simple way of upgrading the wet strengthcharacteristics of a paper without increasing the loading of wetstrength additive. The addition of the perepiquat produces an almostlinear improvement in wet strength at least at proportions below about60 weight %, so that prediction of the amount of perepiquat additiverequired to attain a given wet strength is relatively simple. This isalso a strong indication that the cure mechanisms of the components areindependent of one another and that therefore the differences betweenperepiquat polymers and conventional polyamine/epichlorohydrin additivesare not merely of degree but of kind.

EXAMPLE 13

This Example explores the effect of dilution on the gel time with theobject of finding whether a polymer, prepared at the kind of temperaturethat is conventional in the prior art, (25° C. initially raised to 50°C.) has a gel time that compares to that of a perepiquat resin. For thesake of comparison a perepiquat polymer was obtained under identicalconditions except that the temperature was maintained at 5°-10° C.

Identical amounts of poly(N-methyldiallylamine hydrochloride salt),which had been separated from unreacted monomer, were reacted withidentical amounts of epichlorohydrin at an E/A ratio of 1.70 and a totalsolids concentration of 5%. The first reaction was initiated at 5° C.and allowed to rise to 10° C. over a 48 hour reaction time and thesecond was initiated at 25° C. and then raised to 50° C. for a 6 hourreaction period.

At the end of each reaction the mixtures were acidified with identicalamounts of sulphuric acid. The yield of the first and second reactionswere 84.2% and 81.1% respectively with corresponding epichlorohydrinconversions of 81.5% and 73%.

Solutions of the two polymers each containing 1 gm. of the polymer wereconcentrated to about 8 gm of solution in vacuo on a Buchi Rotavaporatorusing a 250 ml round-bottomed flask, a 30° C. water bath and anaspirator vacuum of 15 mm of mercury. The resin solutions were eachdiluted to 9.3 g with deionized water and transferred to 10 ml. beakers.

To each stirred solution was added 0.88 ml. of 25% aqueous sodiumhydroxide over a period of 5 seconds. These activated solutions were setaside at room temperature and observed for viscosity increase leading togelation.

The polymer prepared at 5°-10° C. (perepiquat polymer) gelled after anaverage of 1583 minutes whereas the polymer produced at 25°-50° C.gelled after an average of 6 minutes 40 seconds.

It would appear therefore that producing the polymers at low dilutiondoes nothing to reduce the differences between perepiquat polymers ofthe invention and those polymers prepared at temperatures of theprocesses of the prior art.

The above Examples are presented for the purposes of illustration of theperepiquat polymers of the invention and the manner of their productionand are not intended to imply any limitation on the scope of theinvention described herein.

It is foreseen that a number of non-essential variations andmodifications could be made to the compositions and processes describedherein without departing from the basic invention. It is intended thatall such modifications and variations be embraced within the purview ofthis invention.

What is claimed is:
 1. A process for improving the wet strength of acellulosic substrate which comprises:I. providing a compositioncomprising water-soluble, cationic, thermosetting polymer comprising abackbone formed of repeating segments, at least 10% of which comprise anamine group, whereinA. substantially all the amine groups are pendantfrom the backbone segment and have a structure selected from the groupconsisting of ##STR11## wherein R¹ is selected from the group consistingof methyl and, where the nitrogen bears two R¹ groups these, togetherwith the nitrogen can form a heterocyclic radical; R" is a divalentradical; R'" is a trivalent radical; and R is selected from ##STR12##wherein X is a potential anion; the unattached bond in each aminestructure being attached directly to a carbon atom of the polymerbackbone; and B. a 10% solids solution of the said polymer in water at20° C. and a pH of 11 does not gel for at least 10 hours; II. activatingthe composition by raising its pH to about 10 to 13; III. applying aneffective amount of the activated composition to the substrate; and IV.curing the composition by the application of heat.
 2. The process ofclaim 1 in which at least 10% of the repeating units have the structure##STR13## where Y.sup.⊖ is an anion.
 3. The process of claim 1 in whichat least 10% of the repeating units have the structure: ##STR14## whereg is 1 to
 3. 4. The process of claim 1 in which at least 10% of therepeating units have the structure: ##STR15##
 5. The process accordingto claim 1 in which the polymer is a homopolymer.
 6. A process accordingto any one of claims 1 to 5 in which the polymer is applied at a levelof 0.5 to 20 kilos of polymer per metric ton of the substrate.
 7. Aprocess for improving the wet strength of a cellulosic substrate whichcomprises(1) forming a composition comprisingA. from 10 to 90% by weightof a water-soluble cationic thermosetting polymer comprising a backboneformed of repeating segments, at least 10% of which comprises an aminegroup, wherein(A) substantially all the amine groups are pendant fromthe backbone segment and have a structure selected from the groupconsisting of: ##STR16## wherein R¹ is selected from the groupconsisting of methyl and, where the nitrogen bears two R¹ groups, thesetogether with the nitrogen can provide a heterocyclic radical; R" is adivalent radical and R'" is a trivalent radical; and R is selected from##STR17## where X is a potential anion; the unattached bond in eachamine structure being attached directly to a carbon atom in the polymerbackbone; and (B) a 10% solids solution of the said polymer in water at25° C. and a pH of 11 does not gel for at least 10 hours; B. from 90 to10% by weight of a compound different from Component A and containing aplurality of amine groups capable of reacting with epoxy groups fromComponent A; all percentages being based on the solids weight of thecomposition; (ii) activating the mixture raiding its pH to about 10 to13; and (iii) applying the activated mixture to the substrate.
 8. Aprocess according to claim 7 in which component B is a polymer formed byreacting an epihalohydrin with a polymer containing a plurality of aminegroups under such conditions that the transition ratio is not exceeded.9. A process according to either of claims 7 and 8 in which the mixtureis applied at a level of 0.5 to 20 kilos per metric ton of substrate.